The lithium ion capacitor is expected as being substituted for the electric double layer capacitor or the secondary battery. This lithium ion capacitor is an energy storage capacitor, energy storage efficiency of which is remarkably enhanced by utilizing physical phenomenon of pre-doping of ion to negative electrode. At the present time, the electric double layer capacitor has been used for storing electricity generated by a cell motor in a large-sized machine such as a train and a construction machine but will be expected in the near future as being applying it to an energy storage in fuel cell for a vehicle or the like by downsizing thereof.
The lithium ion capacitor has asymmetrical electrode structure. Accordingly, it has merits such that its voltage is higher than that of the electric double layer capacitor, its internal resistance is less than that of the secondary battery, charge and discharge are carried out for a short time of period, and any degradation by the charge and discharge is limited so that it has a long life for goods. The lithium ion capacitor, however, has demerit of less energy density. The capacitor includes a roll type capacitor, a laminate type capacitor and the like, and each has two electrodes of positive and negative electrodes.
The two electrodes which the lithium ion capacitor has are respectively composed of different species of metals. For example, Al or the like is used as a lead electrode for positive electrode and Cu or the like is used as a lead electrode for negative electrode. When a large amount of discharge energy is required, parallel connection thereof is used whereas when high voltage is required, series connection is used.
As a connecting method of the lead electrodes which are used in the conventional electric double layer capacitor, lithium ion capacitor and secondary battery of laminate type, there are a connecting method of them in which foil-like lead electrodes are used and they are connected by spot-welding using ultrasonic wave or the like (see a patent document 1), a method of connecting them by bodies of revolution contacting the lead electrodes while being pressed (see a patent document 2) and a method of fastening the foil-like lead electrodes by a bolt or the like.